1. Field of the Invention
The present invention relates to a positive-working or negative-working radiation-sensitive mixture and to a recording material having a substrate and a coating including the mixture. In particular, the recording material is suited for making offset printing plates.
2. Description of Related Art
Radiation-sensitive or light-sensitive mixtures based on naphthoquinone-2-diazide compounds as well as their use in recording materials such as photoresists or presensitized offset printing plates have been frequently described in the literature. The imagewise exposure of such materials proceeds with radiation sources emitting radiation in the absorption range of the quinone diazides, i.e., in the range of about 350 to 450 nm. The imagewise exposure is usually followed by a processing or developing step. Aqueous alkaline solutions based on alkali silicates are widely used as developers in making printing plates. The processed printing plates may be treated with an appropriate correction solution, and if they are not intended for immediate use on the printing press, preservation with a hydrophilic agent is advantageous.
As a result of the further development of the art, high-power, low-cost infrared light sources basically suited for direct imaging of recording materials have been provided. In particular, laser diodes emitting radiation at a wavelength of about 800 nm, and Nd:YAG lasers emitting radiation at a wavelength of about 1064 nm are mentioned. Furthermore, the use of carbon as an IR absorbing component has been disclosed (e.g., in WO 96/20,429). Carbon absorbs IR radiation throughout a wide wavelength range. So far, the use of carbon or carbon pigments in the radiation-sensitive coating of the recording materials as described above have failed because the recording materials after the imagewise IR exposure could not be processed regularly with an aqueous alkaline developer. The processing was often found to be incomplete, i.e., the residual radiation-sensitive coating was left on the radiation-exposed or radiation-unexposed areas.